Semiconductor devices are typically fabricated through fabrication processes including a thin film process, a photolithography process, an etching process, a diffusion process, and the like. The fabrication of most compound semiconductor devices begins with growth of semiconductor thin films onto a substrate using deposition techniques. It can be extremely difficult to monitor the growth of semiconductor thin films in a vacuum chamber. Surface diagnostic tools must operate in ultra-high vacuum environments, making them unusable for semiconductor growth chambers. Semiconductor coverages of only a few molecular layers are particularly difficult to monitor (sense). These growth processes are, by definition, surface chemistry issues which can be difficult to obtain accurate quantitative status of the growth process. Damaged interfaces, such as those caused by whisker formation, can only be identified after the processing is complete.
Existing monitoring solutions are mostly based on heuristic and historical processes. There are some in-situ diagnostic solutions which show only that some characteristic has changed, but are incapable of identifying what has changed. Current diagnostic systems are typically ex-situ and only identify problems well after the in-process device (e.g., wafer) has been rendered defective. As a result, there is currently no way to identify and potentially correct any unwanted growth process during processing.
Accordingly, there is a need for a monitoring system which addresses the drawbacks identified above.